This invention relates to novel compunds of calcium, titanium, zirconium and oxygen which have been found very useful, particularly as pigments, and to processes for preparing such compounds.
Pigments have been widely used for a large variety of purposes for milennia. During this period, a great many materials have been tried as pigments with greater or less success and at the present time a considerable number of materials are in commerical use as pigments. It will be appreciated, however, that all pigments are not suited or usable for all purposes. Thus, for a specific use one pigment may be superior to another because of its better color or its greater hiding power. On the other hand, for another specific use the greater tinting strength of one pigment may cause it to be preferred to another. Consequently, there is a continual search for new pigment materials and for modifications of known pigments which will result in making available for use pigments having novel or improved properties.
Among the known and extensively used pigment materials is titanium dioxide (TiO.sub.2). This material is white and, as a pigment, has very great hiding power. Also previously suggested for use as a white pigment, is zirconium dioxide (ZrO.sub.2). Although this compound is used to a limited extent as a pigment, it suffers from the disadvantages that not only is it considerably more expensive than titanium dioxide, but is also has less covering power and tinctorial strength. Other white or light colored metal oxides have been suggested for use as pigments and some of these such as zinc oxide (ZnO) and antimony oxide (Sb.sub.2 O.sub.3) have been so used, zinc oxide, for example, being employed quite extensively. However, some common, white, metal oxides are substantially lacking in desirability for pigmentary use. Calcium oxide (CaO) is a good example of this. This oxide, while inexpensive, is unusable per se as a pigment because of its chemical reactivity with water and many paint vehicles. Although the reaction product of CaO with water, calcium hydroxide (Ca(OH).sub.2), is used to some extent as a pigment, for example in the so-called "whitewash", the pigmentary properties of the hydroxide are of very low quality.
Although some compositions containing two or more of the oxides TiO.sub.2, ZrO.sub.2, and CaO, including a rare mineral containing all three oxides in substantially the same proportions as the products described herein are known, it has been discovered that novel compounds of these oxides can be produced by the procedure herein disclosed. These novel products, when finely divided, are useful as pigments and one such product provides an excellent white pigment with an unexpectedly good combination of pigmentary properties. In fact, in one respect or another, it is a better pigment than any one of the three constituent oxides.
SUMMARY OF THE INVENTION
The novel, crystalline compounds of the present invention have been found to have a composition that can be represented by the formula CaTiZr.sub.3 O.sub.9, and distinctive x-ray diffraction patterns. One of said novel compounds can be produced from an intimate mixture of calcium carbonate, titanium dioxide and zirconium dioxide in the molar ratio 1:1:3 by calcining the mixture to a temperature of about 1400.degree.C. Another of such novel compounds can be produced by calcining, to a temperature of at least 600.degree.C and not substantially above about 1000.degree.C, a conglomerate which is chemically homogeneous and consists essentially of Ca, Ti, Zr and O and at least one thermally fugitive ligand per atom of metal component, said calcination being for a period of at least 2 hours at 600.degree.C. The Ca, Ti, and Zr in the conglomerate are preferably in the atomic ratios of 1:1:3 and the oxygen is present in amount necessary to form the highest oxide of each of the three metals. The novel compounds when finely divided are useful as pigments. The second mentioned compound, because of its excellent whiteness and covering power, is particularly desirable as a replacement for TiO.sub.2 pigments for certain uses.